Introduction: The temporal relationship between reflux symptoms and reflux episodes during ambulatory reflux monitoring can be studied with symptom association analysis, and the strength of the relationship can be expressed using indices such as the SAP (symptom association probability), SI (symptom index), and SSI (symptom sensitivity index). The reproducibility of these indices has not been determined yet.
Method: Twenty-one patients with typical reflux symptoms (9 men, 53 [38-57] yr) underwent two 24-h combined pH-impedance recordings off acid-secretory medication with an interval of 1-4 wk. The SAP, SI, and SSI were calculated for each measurement. Reproducibility of these indices was determined with Kendall's coefficients of concordance.
Results: The number of reflux events were highly reproducible (Kendall W = 0.92, P < 0.01). The number of symptoms related to reflux events was reproducible (Kendall W = 0.91, P < 0.01) while the number of reported reflux symptoms was not (Kendall W = 0.75, P= 0.07). The SAP and SSI were highly reproducible (Kendall W = 0.90, P= 0.01, and W = 0.86, P < 0.05, respectively) but the SI was not (W = 0.73, P= 0.09). The percentage of patients with similar outcomes on two separate test days for the SAP, SI, and SSI was 86%, 67%, and 86%, respectively.
Discussion: In 24-h pH-impedance recordings of patients with reflux symptoms, the number of reflux events and the number of symptoms related to reflux events were highly reproducible as were the SAP and SSI. This supports the use of these indices to express the relationship between symptoms and reflux episodes in clinical practice.